Kelly bar and mounting means therefor

ABSTRACT

A rotary drill having a driven rotary table with an axially directed passage through its center of rotation defined by a hollow spindle depending from the rotary table. A kelly bar of noncircular cross section extends through the passage. A noncircular face of the kelly bar is engaged for positive rotation with the spindle by a mating piece on the spindle. A circular cross section liquid-tight coupling at the bottom of the kelly bar lies radially within the inner circumference of the noncircular kelly bar. Plungers carried by the spindle selectively engage shoulders on the kelly bar for exerting axial pressure on the kelly bar when the rotary table is moved axially downward.

United States Patent [72] Inventor Charles L. Rassieur 2,693,344 l 1/ 1954 Scott 173/166 University City, Mo. 2,709,572 5/ 1955 Ageborn l73/ 165 [2l] Appl. No. 765,783 2,845,250 7/1958 Ball 173/166 [22] Filed 0ct.8, 1968 3,426,857 2/1969 Bland 173/163 [45] Patented Feb. 9,1971 Primm y Examinerjames A. Leppink [73] Assignee Central Mine Equipment Company St. Louis County, si. Louis M0. Attorney Polster and Polster a corporation of Missouri [54] KELLY BAR AND MOUNTING MEANS THEREFOR ABSTBACT A rotary drill having a dlIVCn IOial'y table with 14 Claimssnrawlngplgs. an axially directed passage through its center of rotation defined by a hollow spindle depending from the rotary table. [52] U.S. Cl. 173/166, A llly bai. of noncirculall cross section extends through the 175/ 195 passage. A noncircular face of the kelly bar is engaged for [5l] Int.Cl. E2lb3/04 positive rotation with the spindle by a mating piece on the [50] Field ofSearch 173/163, spindli A circular cross Section liquid tighl coupling at the 166 1659 175/113 114 195 bottom of the kelly bar lies radially within the inner circum- 56 i R f Ct d ference of the noncircular kelly bar. Plungers carried by the 'I l e "ences l e spindle selectively engage shoulders on the kelly bar for exert- UNITED STATES PATENTS ing axial pressure on the kelly bar when the rotary table is 2,294,318 8/1942 Rich `175/195 moved axially downward.

l I I l i 6| 5| v I5 i M "f l Il KELLY BAR AND MOUNTING MEANS THEREFOR BACKGROUND OF Tl-IE INVENTION This invention relates to a drilling apparatus having a kelly 5 bar rotated by a rotary table.

Presently known rotary drills of the type having a rotary table mounted several feet from the ground and a noncircular kelly bar mounted through a central axial passage in the rotary table, have traditionally included a bowl attached to the top of the table and a drive bushing having an internal noncircular aperturewhich mates with the kelly bar. The drive bushing slides over the kelly bar and fits into the bowl, where it is secured. Rotary motion is transferred from the rotary table to the kelly bar through the bowl and drive bushing, and free axial movement of the kelly bar relative to the rotary table is allowed.

The kelly bar is usually a length of round tubing, axially splined to define axially extending flutes and fillets through most of its length. Protruding keys in the drive bushing mate with the flutes in the kelly bar. Other shapes are also used, as for example kelly bars which are square or hexagonal in cross section. For simplicity, the term channel" will be used herein to designate any long, axially extending feature on the surface of the kelly bar, such as a flute or flat, which in a cross section of the kelly bar lies within the circumference of a circle circumscribed about the cross-sectional shape. The term land designates any such axial feature, such as a fillet or edge, which lies on the circumference of such a circle.

The kelly bar and drill rods attached to its lower end are made hollow for receiving a drilling fluid. This fluid enters the drill string at the top of the kelly bar, passes through the bit at the bottom of the drill string and carries cuttings to the surface through the annulus between the drill rod and the drill hole.

In soft drilling formations, the weight of the kelly bar and drill rod is sufficient to provide enough downward force for drilling. When the weight of the drill string is not sufficient for adequate penetration, additional thrust may be supplied either by applying force to a thrust bearing on the top of the kelly bar or by clamping the kelly bar to the rotary table and supplying vertical movement to the rotary table. The former method has the disadvantages of complicating the problem of coupling a drilling fluid conduit to the kelly bar, of introducing considerable wear by requiring parts which must move relative to each other, and of placing considerable strain on the entire length of the kelly bar. The latter method has heretofore in volved the use of a chuck, mountedon the rotary table, having jaws which grip the smooth surface of the kelly bar and transmit vertical force from the rotary table to the kelly bar. The amount of thrust that can be transmitted by the jaws without slippage is limited. Furthermore, this arrangement causes excessive wear on both the jaws and the kelly bar. lf the jaws are activated by a manually tightened screw, the job of tightening and loosening the jaws is quite time consuming. lf, however, an automatic chuck which hydraulically closes the jaws or a lever operated mechanical chuck'is used, not only is the initial cost high, but, because parts of the chuck remain stationary when the rotary table is turning, the relative movement of parts within the chuck tends to wear it out.

One of the objects of this invention is to provide a kelly bar and means for attaching it to a rotary table which do not require the use of a bowl or drive bushing.

Another object is to provide a kelly bar and means for mounting it through a rotary table which allow selective positive transmission of vertical force from the rotary table to the kelly bar.

Another object is to provide such a kelly bar and mounting means which are inexpensive to manufacture and rugged in use.

Other objects will occur to those skilled in the art in the light of the following description and accompanying drawing.

SUMMARY OF THE INVENTION In accordance with this invention, generally stated. a rotary drilling apparatus having a driven rotary table with an axially directed passage through its center of rotation and a kelly bar extending through the passage is provided in which axially extending channels and lands are provided on the kelly bar, with the channels extending to the lowermost edge of the lands. An adapter is secured to the lower'end of the kelly bar for attaching a drill rod to it. ln the preferred embodiment` the lower end of the kelly bar is externally threaded, the outer circumference of the threads being radially outboard of the inner circumference of the channels in order to give the greatest possible strength. The channels extend through the threads, and the threaded connection is therefore not waterproof; accordingly a sealing section is provided imboard of the inner circumference of the channels. In the preferred embodiment the sealing means is an O-ring seal on a protruding nipple on the end of the kelly bar, which mates with an inner surface on the adapter.

Also in the preferred embodiment the passage through the rotary table is defined by a hollow spindle, secured to the upper face of the rotary table by a single nut and depending from the rotary table. Keys adapted to engage the channels on the kelly bar are permanently mounted in the lower end of the spindle. The kelly bar may therefore be inserted through the top of the rotary table and the adapter thereafter threaded onto the kelly bar, without the necessity of a drive bushing.

The kelly bar is provided with shoulder means having a radial surface and plunger means are provided on the rotary table for selectively engaging the shoulder means.

In the preferred embodiment, the shoulder means are milled slots in the lands, extending transversely of the kelly bar axis, and the plunger means are movable plungers continuously spring biased toward the milled slots.

In a first preferred embodiment the milled slots are provided with squared upper and lower surfaces, the lower -surface defining the shoulder means, and the plungers can be disengaged from the slots only by rotation of disengagement cams to retract the plungers against the bias of the springs.

ln a second preferred embodiment the upper faces of the milled slots are angled to form a camming surface for automatically disengaging the plungers from the milled slots when the rotary table is raised vertically, but allowing the plungers to be moved by the bias of the springs into the next set of milled slots on the kelly bar.

BRIEF DESCRIPTION OF THE DRAWING In the drawing, FIG. 1 is a view in front elevation, partially interrupted, of one illustrative embodiment of kelly bar and mounting means of this invention;

FIG. 2 is an enlarged sectional view 'taken through the long axis ofthe kelly bar and mounting means shown in FIG. l;

FIG. 3 is a sectional view taken along the line 3-3 of FIG. 2;

FIG. 4 is a sectional view taken along the line 4-4 of FIG. 2; and

FIG. 5 is a detail in front elevation, cutaway, of a second illustrative embodiment of kelly bar and :mounting means of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, and in particular to FIGS. l- 4, reference numeral l indicates one illustrative embodiment of kelly bar of this invention, and reference numeral 3l indicates a mounting means for the kelly bar l.

The kelly bar 1 is in the form of a tube 3, circular in cross section, the outer surface of which is axially splined to form a pair of diametrically opposed flutes 5.. The flutes 5 define a pair of iillets`7 on the surface of the tube 3.

The lutesjS terminate a short distance from the upper end of the tube 3, in thisl illustrative embodiment, about four inches from the top of the tube 3. An internally threaded section is provided in the tube 3 above the flutes 5, for making connection with a water swivel, not shown, for injecting drilling tiuid into the kelly bar.

At spaced axial intervals the fillets 7 on the tube 3 are provided with pairs of parallel milled slots 9 extending transversely of the axis of the tube 3. Each milled slot 9 provides a lower shoulder 11 and an upper shoulder 13 on the tube 3. The outer edges ofthe shoulders 11 and 13 are beveled slightly. ln this illustrative embodiment the kelly bar is about l 16 inches long, the upper pair of slots 9 is spaced axially about 2O inches from the top of the kelly bar, and three other pairs of slots are axially spaced at 30 inch intervals. The lowest pair of slots 9 is therefore about 6 inches from the bottom of the kelly bar. Also in this illustrative embodiment the slots have an axial width of about l inch and a radial depth of about seven-sixteenths of an inch.

About 2 inches below the lowest pair of slots 9, the tube 3 is provided with an annular rabbet 16 having a radial depth of about one-fourth of an inch. Below the rabbet 16, an external thread 19`is cut in the tube 3` In this illustrative embodiment the thread 19 is cut about 0.0i inch deeper than the flutes S.

About an inch from the bottom of the tube 3 the flutes 5, the fillets 7 and the threads 19 terminate in a shallow annular shoulder 18. The short section of the tube 3 which depends from the shoulder 18, forms a nipple l5. An O-ring 17 is seated in a channel in the outer face of the nipple 15.

An adapter 21 is provided having internal threads 23 adapted to mate with the threads 19 on the kelly bar l at one end and internal threads 24 at the other end to receive the upper end of a drill rod. The outer diameter of the adapter 21 is the same as that of the fillets 7 on the kelly bar 1. The upper end 25 of the adapter mates with the annular rabbet 16 on the kelly bar 1. Between the threads 23, and the threads 24 a wall 27 has a slightly larger inner diameter than the outer diameter of the nipple l and is adapted to form a fluid tight fit with the O-ring 17. An annular bevel 29 between the threads 23 and the wall 27 eases the fit of the O-ring 17 into the adapter.

The kelly bar mounting means 31 includes a rotary table 33 supported by a yoke 35. The yoke 35 is mounted on a pair of slide tubes 36, which are slidably mounted on a pair of hydraulic cylinders 37 for vertical motion thereon. A pair of support rods 39 secured to the yoke 35 transmit the motion of pistons 38 in the hydraulic cylinders 37 to the yoke 35. The rotary table 33, is rotated about its axis by a standard power transfer from the drill engine, not shown. A hollow spindle 41 extends through the rotary table 33, for rotation with the rotary table 33. At its upper end, the spindle 41 is held to the rotary table 33 by a large nut 45 threaded onto the spindle 41. An annular flange 47 is welded to the lower edge of the spindle 41. A chuck 51 is bolted to the flange 47. The chuck 51 includes a solid body part S3 having a central bore S5 of somewhat smaller diameter than the inner diameter of the spindle 41, so as to form a closer tit with the kelly bar 3. Axially extending keyways 57 are machined in the bore on diametrically opposed sides of the bore 55. A pair of keys 59 are mounted in the keyways 57 and held by bolts 6l extending through the body part 53 of the chuck 51. The free ends of the keys 59 are adapted to form a slidable fit with the'flutes S on the kelly bar l.

At the axial center of the chuck body 53 a pair of radially extending bores 63 are provided, having a common axis perpendicular to that of the keys 59. A closure plate 65 is welded to the inner end of a counterbore 67 at the outer end of each bore 63. Plungers 69 are slidably mounted in bores 63. The inner ends of the plungers 69 are provided with bottom tiats 7l and top flats 73 and are proportioned to be extensible into the milled slots 9 in the kelly bar 1 when the plungers 69 are moved inward. When the plungers 69 are moved into the milled slots 9 and the chuck 51 moved downward, the bottom flats 71 on the inner ends of the plungers 69 abut radially extending lower shoulders 11 of the milled slots 9, The plungers 69 are biased inward toward the kelly bar l by springs 7S jour naled in the plungers 69 and bearing against the closure plates 65.

The plungers 69 are movable out of engagement with the kelly bar 1 by means of camming devices 81 attached to tails 77 on the plungers 69. The tails 77 pass through central apertures 79 in the closure plates 65. The cammingdevices 81 consist of U-shaped cams 83 having parallel upstanding ears 85 and a central web section 87. The ears 85 are pivotally mounted to the tails 77 on the plungers 69 by pins 89, and the outer surfaces of the ears 85 form camming surfaces for bearing against the outer faces of the closure plates 65. Handles 91 are secured to the central web sections 87 of the cams 83 for rotating the cams 83. Slots 93 in the chuck body above and below the counterbores 67 allow the handles 91 to move from an upward plunger-in stop position to a downward plunger-out stop position.

ln operation, the kelly bar l may be inserted into the spindle 41 through the top of the rotary table 33. The adapter 2l is then threaded onto the lower end of the kelly bar l and a drill rod attached to the adapter 21. For drilling in relatively soft formations, the plungers 69 may be left retracted and drilling commenced utilizing only the weight of the kelly bar and drill rod for vertical force. Drilling fluid may be utilized in a conventional manner.

1t will be noted that the entire chuck rotates with the kelly and drill rod and that the entire rotational force is borne by the keys 59. The kelly bar is freely slidable vertically.

When use of additional vertical force becomes necessary` the handles 91 are pulled up to release the plungers 69 and the rotary table 33 is hydraulically raised on the hydraulic cylinders 37 until the plungers 69 spring into the first set of'milled slots 9 which they encounter. When the rotary table 33 is then hydraulically lowered, the lower edges 71 of the plungers 69 engage the shoulders l1 on the slot 9 and transmit the downward force of the rotary table to the kelly bar and drill rod.

It will be noted that the inner ends of the plungers 69 need not, and preferably do not, contact the inner walls of the slots 9. The entire torsional force is still taken by the keysf59, and the entire vertical force is taken through the plungers 69. There is still no relative movement of any of the parts of the chuck.

When the rotary table has moved to the bottom of its travel, the plungers arey withdrawn, the rotary table raised a `few inches, and the plungers again released. The rotary table is then raised. When the next set of milled slots is reached, the plungers engage the slots and the rotary table may be lowered again.

With the plungers 69 disengaged, the kelly can be raised in a conventional manner by a winch line attached to a bail on the water swivel at the top of the kelly bar. lf the drill string is to be pulled by hydraulically raising the rotary table, the plungers may be released into the slots in the kelly bar. The upper faces 73 of the plunger bear against the upper shoulders 13 of the slots 9 and transmit the upward thrust to the drill string.

A second embodiment of kelly barv and mounting means of this invention is shown in FIG. 5. This illustrative embodiment is identical with that shown in FIGS. 1-4 in both constructiony and operation, except that the upper shoulders 113 offthe milled slots 109 in its kelly bar 101 are beveled to form camming surfaces rather than being square as are the shoulders 13 in the first illustrative embodiment. This embodiment has the advantage over the first illustrative embodiment that when additional force must be applied to the kelly bar the plungers can be released at the beginning of the first stroke and will automatically disengage themselves from a slot 109 when the rotary table is raised and engage another slot 109 when the rotary table is lowered, without requiring manual withdrawal and release of the plungers. However, the rotary table cannot be used for raising the kelly bar in this embodiment or for holding the kelly bar when a drill rod section is added.

Numerous variations in the kelly bar and mounting means of this invention, within the scope of the appended claims. will become apparent to those skilled in the art in the light of the foregoing disclosure.

lclaim: l

l. In a rotary drilling apparatus wherein a rotary table is adapted to be moved axially while rotating, said rotary table having an axially directed passage through it at its center of rotation, a kelly bar extending through said passage and means carried by the rotary table for providing positive rotational force transmission from the rotary table to the kelly bar, the improvement comprising shoulder means on said kelly bar having a radial shoulder surface, plunger means carried by said rotary table for selectively engaging and disengaging said kelly bar shoulder surface, and actuating means carried by said rotary table for causing said plunger means to engage and disengage said shoulder surface, saidplunger means having an axially lower surface which positively bears upon said shoulder surface when the rotary .table is moved axially downwardly and the plunger means are-in shoulder surface engaging position.

2. The improvement of claim 1 wherein the plunger means comprise plungers movably mounted and continuously spring biased toward shoulder surface engaging position.

3. The improvement of claim 2 wherein a plunger camming surface extends upwardly from the shoulder surface of the kelly bar whereby the kelly bar can move downwardly past the inwardly biased plungers but cannot move upwardly therepast when the plungers are in shoulder surface engaging position.

4. The improvement of claim 2 wherein the actuating means comprise camming means on the plungers for selectively holding the plungers out of shoulder surface engaging position and allowing the plunger to move into shoulder surface engaging position.

5. The improvement of claim 1 wherein the kelly bar is splined to define axially extendingflutes and fillets and said means carried by the rotary tablerfor providing positive rotational force transmission from the rotary table to the kelly bar comprise keys projecting into said flutes.

6. The improvement of claim 5 wherein the flutes extend to the bottom edge of the fillets. y

7, The improvement of claim 1 including a hollow spindle mounted in the passage through the rotary table, said means for providing positive rotational force transmission from the rotary table to the kelly bar and said plunger means being mounted on the lower end of the spindle.

8. The improvement -of claim l wherein the kelly bar is hollow, and externally threaded at its lower end, and includes axially extending channels and lands extending substantially the entire length of the kelly bar, the outer circumference of the threads being radially outboard of the inner circumference of the channels and said channels extending axially through said threads, and including an adapter having internal threads, complementary to the threaded endv of the kelly bar, and sealing means on said adapter and kelly bar for forming a liquidtight seal between said adapter and kelly bar, said sealing means having an inner circumference no larger than the inner circumference of said channel.

9. A rotary drilling apparatus comprising a rotary table which is axially movable while rotating, said rotary table having an axially directed passage through it at its center of rotation, and a chuck mounted on said rotary table for rotation therewith, said chuck comprising a body part having a central axial bore coaxial with said axially directed passage of said rotary table; a pair of diametrically opposed keys mounted on said body part and extending into said bore; and a pair of diametrically opposed plungers mounted in said body part, said plungers being extensible into and retractable out of said bore.

l0. ln a rotary drilling apparatus wherein a rotary table is adapted to be moved axially while rotating, said rotary table having an axially directed passage through it at its center of rotation, and a kelly bar extending through said passage, the improvement comprising shoulder means on said kelly bar having a radial shoulder surface and plunger means carried by said rotary table for selectively engaging said kelly bar shoulder surface, said plunger means having an axially lower surface which positively bears upon said shoulder surface when the rotary table 1s moved axially downwardly' and the plunger means are in shoulder surface engaging position, said kelly bar being splined to define axially extending flutes and fillets, said flutes extending to the bottom edge of said fillets` means carried by the rotary table for providing positive rotational force transmission from the rotary table to the kelly bar comprising keys projecting into said flutes, and a hollow spindle mounted in the passage of the rotary table, said keys being mounted on the lower end of the spindle.

1l. The improvement of claim 10 wherein the kelly bar is hollow, and externally threaded at its lower end, and includes an adapter having internal threads, complementary to the threaded end of the kelly bar, said adapter being mounted on said kelly bar, and means on said adapter and kelly bar for forming a liquid tight seal between saidl adapter and kelly bar.

l2` In a rotary drilling apparatus wherein a rotary table is adapted to be moved axially while rotating, said rotary table having an axially directed passage through it at its center of rotation, and a kelly bar extending through said passage, the improvement comprising shoulder means on said kelly bar having a radial surface and plunger means carried by said rotary table for selectively engaging said kelly bar shoulder surface, said plunger means having an axially lower surface which positively bears upon said shoulder surface when the rotary table is moved axially downwardly and the plunger means are in shoulder surface engaging position; a hollow spindle mounted in the passage of the rotary table, and a chuck mounted on the lower end of said spindle, said plunger means being mounted in said chuck.

13. The improvement of claim l2 wherein the kelly bar is splined to define axially extending flutes and lands, and keys carried by said chuck project into said flutes.

14. The apparatus of claim 9 further comprising a kelly bar extending through said passage, said kelly bar having a pair of flutes respectively engaged by said pair of keys and a pair of transverse slots proportioned to receive respectively said pair of plungers when said plungers are extended into said bore. 

1. In a rotary drilling apparatus wherein a rotary table is adapted to be moved axially while rotating, said rotary table having an axially directed passage through it at its center of rotation, a kelly bar extending through said passage and means carried by the rotary table for providing positive rotational force transmission from the rotary table to the kelly bar, the improvement comprising shoulder means on said kelly bar having a radial shoulder surface, plunger means carried by said rotary table for selectively engaging and disengaging said kelly bar shoulder surface, and actuating means carried by said rotary table for causing said plunger means to engage and disengage said shoulder surface, said plunger means having an axially lower surface which positively bears upon said shoulder surface when the rotary table is moved axially downwardly and the plunger means are in shoulder surface engaging position.
 2. The improvement of claim 1 wherein the plunger means comprise plungers movably mounted and continuously spring biased toward shoulder surface engaging position.
 3. The improvement of claim 2 wherein a plunger camming surface extends upwardly from the shoulder surface of the kelly bar whereby the kelly bar can move downwardly past the inwardly biased plungers but cannot move upwardly therepast when the plungers are in shoulder surface engaging position.
 4. The improvement of claim 2 wherein the actuating means comprise camming means on the plungers for selectively holding the plungers out of shoulder surface engaging position and allowing the plunger to move into shoulder surface engaging position.
 5. The improvement of claim 1 wherein the kelly bar is splined to define axially extending flutes and fillets and said means carried by the rotary table for providing positive rotational force transmission from the rotary table to the kelly bar comprise keys projecting into said flutes.
 6. The improvement of claim 5 wherein the flutes extend to the bottom edge of the fillets.
 7. The improvement of claim 1 including a hollow spindle mounted in the pAssage through the rotary table, said means for providing positive rotational force transmission from the rotary table to the kelly bar and said plunger means being mounted on the lower end of the spindle.
 8. The improvement of claim 1 wherein the kelly bar is hollow, and externally threaded at its lower end, and includes axially extending channels and lands extending substantially the entire length of the kelly bar, the outer circumference of the threads being radially outboard of the inner circumference of the channels and said channels extending axially through said threads, and including an adapter having internal threads, complementary to the threaded end of the kelly bar, and sealing means on said adapter and kelly bar for forming a liquid-tight seal between said adapter and kelly bar, said sealing means having an inner circumference no larger than the inner circumference of said channel.
 9. A rotary drilling apparatus comprising a rotary table which is axially movable while rotating, said rotary table having an axially directed passage through it at its center of rotation, and a chuck mounted on said rotary table for rotation therewith, said chuck comprising a body part having a central axial bore coaxial with said axially directed passage of said rotary table; a pair of diametrically opposed keys mounted on said body part and extending into said bore; and a pair of diametrically opposed plungers mounted in said body part, said plungers being extensible into and retractable out of said bore.
 10. In a rotary drilling apparatus wherein a rotary table is adapted to be moved axially while rotating, said rotary table having an axially directed passage through it at its center of rotation, and a kelly bar extending through said passage, the improvement comprising shoulder means on said kelly bar having a radial shoulder surface and plunger means carried by said rotary table for selectively engaging said kelly bar shoulder surface, said plunger means having an axially lower surface which positively bears upon said shoulder surface when the rotary table is moved axially downwardly and the plunger means are in shoulder surface engaging position, said kelly bar being splined to define axially extending flutes and fillets, said flutes extending to the bottom edge of said fillets, means carried by the rotary table for providing positive rotational force transmission from the rotary table to the kelly bar comprising keys projecting into said flutes, and a hollow spindle mounted in the passage of the rotary table, said keys being mounted on the lower end of the spindle.
 11. The improvement of claim 10 wherein the kelly bar is hollow, and externally threaded at its lower end, and includes an adapter having internal threads, complementary to the threaded end of the kelly bar, said adapter being mounted on said kelly bar, and means on said adapter and kelly bar for forming a liquid tight seal between said adapter and kelly bar.
 12. In a rotary drilling apparatus wherein a rotary table is adapted to be moved axially while rotating, said rotary table having an axially directed passage through it at its center of rotation, and a kelly bar extending through said passage, the improvement comprising shoulder means on said kelly bar having a radial surface and plunger means carried by said rotary table for selectively engaging said kelly bar shoulder surface, said plunger means having an axially lower surface which positively bears upon said shoulder surface when the rotary table is moved axially downwardly and the plunger means are in shoulder surface engaging position; a hollow spindle mounted in the passage of the rotary table, and a chuck mounted on the lower end of said spindle, said plunger means being mounted in said chuck.
 13. The improvement of claim 12 wherein the kelly bar is splined to define axially extending flutes and lands, and keys carried by said chuck project into said flutes.
 14. The apparatus of claim 9 further comprising a kelly bar extending through said passage, said kelly bar having a pair of flutes respectively engaged by said pair of keys and a pair of transverse slots proportioned to receive respectively said pair of plungers when said plungers are extended into said bore. 